Generally speaking, bandwidth is the range of frequencies that a communications system, for example, a carrier network, is capable of carrying along its transmission medium. As each communication channel provided by the carrier network consumes a portion of the network's bandwidth, the bandwidth of the carrier network limits the number of communication channels which it can provide to its subscribers.
Different types of communications require different bandwidths. For example, one video channel requires approximately the same bandwidth as 1,200 voice telephone channels. In order to provide a single system capable of carrying the various types of communications, carrier networks are gradually evolving towards architectures such as asynchronous transfer mode (or "ATM") which will provide variable bandwidth to subscribers. It is contemplated that such networks will be particularly well suited for transmission of various types of media--voice, data, image and video--each requiring a different amount of bandwidth to complete the transmission.
An important concept in ATM is Quality of Service (or "QoS"). QoS defines the standards to which an ATM provider will adhere to when providing service to a subscriber. Based upon its planned usage of the ATM network, a subscriber will enter into a traffic contract with a service provider for a specific amount of bandwidth. Among other things, QoS assures the subscriber that the contracted bandwidth will be available for data transfers at a specified bit rate. Due to the increased cost thereof, a subscriber will rarely contract for bandwidth in excess of their expected usage. Problems may arise, however, if the subscriber attempts to complete a call or other type of connection which, if completed, would result in the subscriber consuming bandwidth in excess of the amount to which he or she had previously contracted for. For example, a subscriber may contract for sufficient bandwidth to complete a single voice channel but then attempt to conduct a video conference. Most service providers do not permit the subscriber to consume excess bandwidth and would, therefore, reject any requested connection which would produce such a result. Such rejections are often based upon the fear that, if the request were accepted, the service provider would not be able to maintain the specified data rate for the connection, thereby resulting in the loss of one or more data calls.